There are a wide variety of individual or mass transport passenger seats providing a variety of adjustability options and configurations to suit the user's need to change the posture of his body whilst seated. Examples of such seats include airline seats, train seats, bus seats, coach seats, and so on. Such seats may be fixed to a floor, or fixed to a frame wherein the frame is fixed to a floor. Typically, such seats are configured to offer a varying degree of fit to the user's morphology, anatomy, or change of posture. Such seats' adjustability options can include seat height adjustability from floor level, seat depth adjustability from front seat edge to base of back rest, backrest angle adjustability in relation to the seating surface, height of lumbar support from seating surface, and backrest height adjustability in relation to seating surface.
One of the simplest forms of seat adjustability is the ability to change the angle of the seat backrest in relation to a fixed seating surface. This is common in aeroplanes, trains and coaches. Reclining the backrest is generally performed by the user manually disengaging some kind of restraint mechanism, exerting pressure on the ground through his legs, and pushing back into the backrest using his back, against the action of a spring or other biasing means, in order to pivot the backrest about a pivot axis located across the rear of the seat pan. When the backrest is at the desired angle, the user re-engages the restraint mechanism. Raising the backrest towards an upright position is achieved by a similar process, allowing the spring or biasing means to assist with bringing the backrest upwards, but nevertheless also requiring the user to maintain pressure through his legs in order to control the motion of the backrest. Both these adjustment procedures, and in particular the reclining of the backrest, can put significant pressure on the user's thighs, and may be uncomfortable.
Additionally, with a conventional fixed horizontal seat pan, tilting the backrest backwards results in the user's body being pushed forward at the hip point and the body tending to slide away from the backrest, which creates a gap at the lower part of the back in which the back is not supported (hence the need to provide supplementary cushions on long haul flights).
More generally, a user of a passenger seat (for example, an airline seat, train seat, coach seat, bus seat, or such like) may experience discomfort during a journey. Whilst conventional reclining seats enable the user to adjust their back angle, they do not generally enable the user to change the pressure points (i.e. the parts of the user's body which bear pressure or stress) during the journey. As a consequence, the user may risk ailments such as deep vein thrombosis, due to the being substantially immobile for a long period of time, without being able to change the pressure points. There is therefore a desire to be able to adjust the pressure points experienced by a user during a journey.
It is also desired to reduce the weight of an aircraft seat. Once multiplied over all the seats in an aircraft, a weight saving may become very significant, and may enable the aeroplane to take off with a lower dead weight, or to use less fuel when flying and thereby reduce operating costs and exhaust emissions, or to carry more cargo.
Further problems relate to the cushions provided on conventional passenger seats. Conventional aircraft seat cushions are usually filled with foam, which can be relatively heavy. Foam cushions can also be relatively flammable, and may give rise to a risk of fire or smoke during a flight. In practice, the flammability of a foam-filled airline seat is often reduced by encasing the foam cushion in a protective fire barrier, but such fire barriers are generally made of an expensive cloth. There is therefore a desire to reduce the weight and the flammability of airline cushions, and also to reduce cost. Conventional foam cushions can also be somewhat unaccommodating for different users' body shapes and body weights; generally a foam cushion is really only suitable for a fairly narrow range of body weights and shapes.